Heat developable light-sensitive elements

ABSTRACT

A heat developable supported light-sensitive element wherein at least one layer thereon contains the silver salt of benzotriazole, a silver halide, or an inorganic halide capable of forming a silver halide by reaction with the silver salt of benzotriazole, a compound which decomposes upon heating to yield a basic material, and a reducing agent. In another embodiment, the layer further contains a compound capable of releasing water by heating. Further described is a process for obtaining a print wherein the heat developable light-sensitive element(s) described above are heated for 1-30 seconds at 120*-170* C.

United States Patent [451 Jan. 18, 1972 @iiitiibd et all [54] HEATDEVELOPABLE LIGHT- SENSITIVE ELEMENTS [72] Inventors: Kirril Ohkubo;Junpei Noguchi; Takao Masuda, all of Ashigara-Kumigun, Kanagawa, Japan[73] Assignee: Fuji Shashin lFiim Knbushiki Keisha,

Kanagawa, Japan [22] Filed: Aug. 8, 1966 [21] Appl. No.: 570,768

[30] Foreign Application Priority Data Dec. 13, 19 65 Japan ..40/76578[52] U.S.Cl ..96/114.1,96/67 [51] Int. Cl ..G03c 1/02, G03c 1/76, G0303/00 [58] Field of Search ..96/76, 95, 67, 94, 66 T, 114.1; ll7/36.8,36.9

[56] References flirted UNITED STATES PATENTS 3,152,904 10/1964 Sorenson..96/95 3,429,706 2/1969 Shepard ..96/95 3,457,075 7/1969 Morgan ..96/67FOREIGN PATENTS OR APPLICATIONS 943,476 12/1963 Great Britain ..96/114.]

Primary Examiner-J. Travis Brown Assistant Examiner-M. F. KelleyAttorney-Semmes and Semmes ABSTRACT Further described is a process forobtaining a print wherein the heat developable light-sensitiveelement(s) described above are heated for l-30 seconds at 120-l 70 12Claims, No Drawings HEAT DEVELUPABLE Lll'GHT-SENSHTKVE lElLEMlENTfi Thepresent invention relates to a light-sensitive element and moreparticularly to a heat developable light-sensitive element containing alight-sensitive silver salt and one which is capable of forming imagesby heating.

In general, the most widely used photographic light-sensitive elementuses silver halide. This is because photographic light-sensitiveelements using a silver halideare generally excellent in the areas ofsensitivity and gradation, as compared with electrophotographiclight-sensitive elements and other light-sensitive elements. However,problems arise when using a silver halide photographic light-sensitiveelement. A developing solution must be employed for developing thephotographic element after exposure and in order to prevent thedeveloped photographic images from being discolored or faded and thebackground thereof from being blackened under usual light, the developedphotographic element must be further subjected to several processingsteps. The latter additional processings are usually called stopping,fixing or stabilizing. As will now be apparent, it is very desirablefrom the point of view of simplicity in processing to obtainphotographic images by a completely dry process in silver halidephotography and further to obtain stable and semipermanently preservableimages without the necessity of fixing and other subsequent processings.

In order to meet this requirement, various efforts have hitherto beenmade. One process is the so-called monobath developing and fixing methodin which the developing and fixing processes of conventional silverhalide photographic processing are conducted in one process. See GermanPat. No. 1,163,142; U.S. Pat. No. 2,875,048 and British Pat. No.954,453.

As another improvement, a process has been provided wherein theprocessing of conventional silver halide photographic elements has beenconducted by a dry system. This system has the advantage that sinceliquid chemicals for development and fixing need not be handled thereare no dangers that hands or clothes may become contaminated with thechemicals as in the case of wet processing and, further, a photograph orcopy can be directly obtained in the dried state. See German Pat. No.1,174,159 and British Pat. Nos. 943,476 and 951,644.

However, the image obtained from conventional heat developablelight-sensitive elements using a silver halide salt become blackened dueto the printing out of the silver halide when the element, afterdevelopment, is placed as is in a light place, which makes thediscrimination of the image dilficult. Therefore, it is necessary insuch a system to process the developed photographic element with astabilizing solution or a fixing solution to make the undeveloped silverhalide particles light-insensitive or convert them into water-solublematerials, which are then removed by washing.

Still other techniques have been proposed in which a silver saltcompound other than silver halide is employed. See U.S. Pat. No.3,152,904 and Belgian Pat. No. 663,1 12.

The present invention relates generally to the last of theaforementioned proposals, i.e., a photographic light-sensitive elementhaving a mixture of a light-insensitive and oxidizing organic silversalt, a slight amount of a light-sensitive silver salt, and moreparticularly to a photographic light-sensitive element containing amixture of a silver salt of benzotriazale and a slight amount of asilver halide.

Accordingly, an object of the present invention is to provide a novellight-sensitive composition.

Another object of the present invention is to provide a novel processfor reproducing images.

Still another object of the present invention is to provide a highlysensitive light-sensitive element capable of forming images by a dryprocess or by only heating without using any solutions in the developingprocess.

A further object of the present invention is to provide alight-sensitive element capable of providing light-stable images bydeveloping, and one which is aiso capable of being preservedsubstantially pennanently after development without the necessary ofconducting fixing and other procedures.

Other objects and advantages of the instant invention will becomeapparent from the ensuing specification.

The heat developable light-sensitive element of the present inventionhas a single-layer or multilayer containing a mixture of an organicsilver salt which is light-insensitive and which can be reduced and avery slight amount of a light-sensitive silver salt, particularly asilver halide.

The light-sensitive element according to one embodiment of the presentinvention comprises a support bearing thereon at least one layercontaining at least (a) a light-insensitive silver salt; (b) a materialfor providing light sensitivity, i.e., a silver halide, or an inorganichalide capable of producing a silver halide by reaction with thelight-insensitive silver salt (a); (c) a compound capable of beingdecomposed into a basic material by heating and, if necessary, acompound capable of releasing water by heating; and (d) a reducingagent.

The light-sensitive element according to another embodiment of thepresent invention comprises a support bearing thereon at least one layercontaining at least (a) a light-insem sitive silver salt; (b) a materialfor providing light sensitivity, i.e., a small amount of a silver halideor an inorganic halide capable of forming a silver halide by reactionwith the light-insensitive silver salt (a); (c) a metal oxide orhydroxide capable of being converted into a basic material by heating;and (d) a reducing agent together with, if necessary, at least onecompound capable of releasing water by heating and a catalyst foraccelerating the oxidation of the reducing agent.

Any of the above-mentioned light-sensitive elements of the presentinvention has color sensitivity and can provide stable images afterexposure by a very simple dry process. Thus, if the images obtained bythe heat development of the light-sen sitive element after exposure arepreserved as they are, the printout of silver halide scarcely proceeds,and moreover, if the thus developed light-sensitive element is processedwith water or other suitable solvent, the progress of printout can becompletely prevented and, hence, permanent images can be obtained.

The support used in this invention may be any physically and chemicallystable flexible sheet such as metal foils, synthetic resin films(generally cellulose diacetate films, cellulose triacetate films,polyethylene terephthalate films, or polycarbonate films) and papers;but among the suitable papers, a paper having a good water-absorbingpower is most suitable for use in the present invention.

As the light-insensitive silver salt, there may be illustrated: silversalts of organic compounds having imino groups, such as a silver salt ofbenzotriazole, a halogen substitute thereof or a nitro substitutethereof, carbazolyl silver, the silver salt of saccharin and the like.Among these salts, the silver salt of the halogensubstituted ornitro-substituted benzotriazole is lightinsensitive but the heatdevelopment thereof is difficult; that is, such a silver salt is noteffectively reduced by heating. Carbazolyl silver is also difficult todevelop by heating. The silver salt of saccharin (o-sulfobenzoic acidimide) may be developed by heating but the contrast between the imageand the background is low; that is, the fonnation of heat fog isincreased. However, in the case of using the unsubstituted silver saltof benzotriazale, it can be developed by heating and the contrastbetween the image and background is high. Further, in the case of usingthe silver salt of benzotriazole, the element can be fixed by bathingwith water, and if the temperature of the heat development is high, thedensity of the background is not increased even if the thusheatrdeveloped light-sensitive element is allowed to stand in usuallight for a long period of time. Accordingly, the silver salt ofbenzotriazole is the most suitable light-insensitive salt for thelight-sensitive element of the present invention.

Thesilver salt of benzotriazole may be prepared by dissolving, forexample, 59.5 g. of 1,2,3-benmtriazole into 2 liters of methanol andadding into the resulting solution an aqueous solution of silver nitrate(85 g./200 ml.) with stirring at normal temperature. The thus-formedprecipitate is washed with water by decantation times, recovered byfiltration, washed with water three times and then dried.

Further, by conducting the reaction of benzotriazole and silver nitratein a solution containing at least one of the belowdescribed binders tobe used for the light-sensitive element, the size of the crystal of thesilver salt can be controlled.

The inorganic halide capable of forming silver halide by reaction withthe light-insensitive silver salt used in this invention is awater-soluble or organic solvent-soluble compound shown by the generalformula hrilX, wherein M represents hydrogen, ammonium or a metal, suchas strontium, cadmium, zinc, tin, chromium, sodium, barium, iron,cesium, lanthanum, copper, calcium, nickel, magnesium, potassium,aluminum, antimony, gold, cobalt, mercury, lead, and beryllium; Xrepresents a halogen atom, such as chlorine, bromine, and iodine; and nis the valency of M. Among them, the iodide is particularly preferablein the present invention since the silver salt formed by the reactionwith the iodide has a property of being difficult to printout.

The light-insensitive organic silver salt containing a small amount of asilver halide or the above-mentioned organic halide may be, after beingdispersed in the below-described binder solution, subjected to a sulfursensitization, a reduction sensitization, or a noble metal sensitizationas in the case of conducting the preparation of conventionalphotographic emulsions to increase the light sensitivity.

The compound to be used in this invention, which can be decomposed byheating into a basic material, can be an oxalate of an aliphatic aminesuch as dicyciohexylamine, an oxalate of an aromatic amine such asbenzylamine, and an oxalate of a cyclic amine such as piperidine andmorpholine. These salts of amines may be prepared by adding an aqueousor alcohol solution of an amine into an excessive amount of an aqueousor alcohol solution of oxalic acid and then filtering, washing anddrying the thus-formed precipitate. These compounds may be used alone oras a mixture thereof.

When such an oxalate of the amine is heated, the oxalate is decomposedto release oxalic acid leaving a suiticient amount of the amine forproviding the basicity necessary for the development.

The oxalates have excellent photographic properties as compared with thesalts of other organic acids and the oxalates may be prepared easily.The decomposition temperature of these salts by heating is about 120 C.for the oxalate of dicyclohexylamine, about 125 C. for the oxalate ofbenzylamine, about 105 C. for the oxalate of piperidine, and about 135C. for the oxalate of morpholine.

The metal oxide or hydroxide employed in the present invention toprovide basicity by heating is the oxide or hydroxide of a metalbelonging to groups 2 or 3 of the periodic table; for example, zincoxide, aluminum oxide, magnesium oxide, zinc hydroxide, aluminumhydroxide, cadmium hydroxide, and magnesium hydroxide.

The above-mentioned metal oxide or hydroxide is also useful as anadditive for improving the contrast between the image and thebackground.

The compound capable of releasing water by heating employed in thisinvention is a compound containing water of crystallization. Among suchcompounds, considering the temperature at which the water ofcrystallization is released and the fitness thereof to photographicemulsions, metal salts of acetic acid, such as lead acetate trihydrate,zinc acetate dihydrate, manganese acetate tetrahydrate, and magnesiumacetate tetrahydrate are very effective. These compounds may be usedalone or as a mixture thereof. The light-sensitive element of thepresent invention containing these compounds capable of releasing waterby heating can provide a good photographic image as compared with thosenot containing such compounds.

The above-mentioned compound containing water of crystallizationreleases a part of the water of crystallization when heated to atemperature lower than 100 C. with the remaining water ofcrystallization being released at about l00 C. By measuring, by adifferential thermal analysis, the temperature at which theabove-mentioned compounds release the water of crystallization, it wasconfirmed that the temperatures are 50 C. and 100 C. for lead acetatetrihydrate, 65 C. and 100 C. for cadmium acetate dihydrate, and C. andl00 C. for zinc acetate dihydrate.

The reducing agent suitable employed in the present invention may be: anaromatic monoor poly-hydroxyl compound or a derivative thereof, or anaromatic monopoly-amino compound or a derivative thereof. For example, adeveloper used for usual photographic processing may be effectivelyused. Particularly effective examples of such reducing agents arehydroquinone, methylhydroquinone, chlorohydroquinone, bromohydroquinone,phenylhydroquinone, catechol, pyrogallol, hydroquinone monosulfonate,resorcinol, paminophenol, o-aminophenol, N-methyl-aminophenol onehalfsulfate, 2-methoxy-4-aminophenol hydrochloride, 2,4- diaminophenolhydrochloride, sodium l-amino-2-naphthol-6- sulfonate, p-oxyphenylglycine, 2-hydroxyethyl-4- aminophenol, N,N-diethyl-p-phenylenediaminesulfite, lnaphthylamine-7-sulfonic acid -acid), M-acid, l-hydroxy-4-methoxynaphthalene, l-hydroxy-4-ethoxynaphthalene, 1,4-dihydroxynaphthalene, and 1-hydroxy-4aminonaphthalene. These compoundsmay be used alone or as a mixture thereof. Besides the above-mentionedcompounds, l-phenyl'3- pyrazolidone, hydroxylamine hydrochloride, andreducing saccharides (glucose, lactose, etc.) may be effectively used asthe reducing agent. For effecting the heat development the oxidationreduction potential must be less than 500 m.v. (a standard hydrogenelectrode).

The blending ratios of the above-mentioned (a) light-insensitive silversalt, (b) light-sensitivity-giving material; that is, the inorganichalide capable of forming a silver halide by reaction with thelight-insensitive silver salt (a) or a small amount of a silver halide;and, in the case of the first embodiment of this invention, (c) thecompound capable of being decomposed by heat into a basic material, and,if necessary, the compound capable of releasing water by heating; or inthe second embodiment of this invention, (c') the metal oxide orhydroxide capable of being decomposed by heating into a basic materialin conjunction with the compound capable of releasing water upon heatingand (d) the reducing agent are generally influenced by the reducingpower, the catalytic power, the molecular weight, and the like, but itis preferable that the proportion of the sensitivity-giving material (b)be from H to l/ 10,000 part by weight based on the weight oflight-insensitive silver salt (a); the proportion of compound (c) befrom 10 to l/ lOO'part by weight based on the weight of thelight-insensitive silver salt (a); the proportion of compound (c) befrom 10 to 1/100 parts by weight based on the weight of thelight-insensitive silver salt (a), the proportion of metal oxide ormetal hydroxide (c') be from 20 to l/ 100 parts by weight based on theweight of light-insensitive silver salt (a), and the proportion ofreducing agent (d) be from 20 to 1/100 parts by weight based on theweight of light-insensitive silver salt (a).

If the proportion of the sensitivity-giving material is larger than theabove-defined value, printing out of the silver halide tends to occur,while if less than the described value, the heat development becomesdifficult. Further, if the proportion of (c) and (c') is larger thandescribed, the preservability of the light-sensitive elements will bereduced, while, if less, the development becomes difficult. Also, if theproportion of reducing agent (d) is larger than the described value,printing out of silver halide tends to occur, while if less than thedescribed value, the development becomes difficult. In the presentinvention, moreover, the composition containing the above-mentionedingredients may contain, if necessary, a color sensitizer, a hardeningagent, a developing accelerator, a matting agent, and a coating aid.

The composition containing the above-mentioned components is applied toa support, such as wood pulp paper, ragcontaining paper, photographicpaper, baryta paper, films, metal foils, dry glass plates, and the like.A part of or the entire composition may be coated on the support inseparate layers. Further, in order to form a uniform and smooth coatingof the composition on the support, it is preferable to use a suitablebinder.

The binder which may be used in this invention is preferably translucentor transparent one so as not to lower the transmission of lighttherethrough. it is particularly preferable to employ photographicgelatin a solid high molecular weight material or resin. Suitable highmolecular weight materials and resins include polyvinyl butyral,cellulose acetate butyrate, polymethyl methacrylate, polyvinylpyrrolidone, ethyl cellulose, polyethylene glycol, polystyrene,polyvinyl chloride, chlorinated rubber, polyisobutylene, a copolymer ofbutadiene and styrene, a copolymer of vinyl chloride and vinyl acetate,a copolymer of vinyl chloride, vinyl acetate and maleic acid,methacrylic resin, polyvinyl alcohol and derivatives thereof such aspolyvinyl acetate.

The color sensitizer, coating aid, color-toning agent, matting agent,hardening agent, etc., may be any of those which are used for thepreparation of conventional silver halide photographic sensitiveelements.

In order to obtain images by using the thus-prepared lightsensitiveelements of this invention, they are, after exposure using as a light.source a tungsten lamp an ultraviolet lamp, heated in a suitable mannersuch as by passing the elements through two heated rollers, by placingthe elements between two heated plates or by the irradiation of theelements with infrared rays.

In the first embodiment of the present invention, the compound capableof releasing water by heating releases water to wet the coating mediumand simultaneously the compound capable of being decomposed by heatinginto a basic material is thermally decomposed to provide basicity to thecoating medium. Consequently, the reducing agent, such as an aromaticmonoor poly-hydroxy compound, is activated and hence the exposed portionof the light-sensitive silver halide having a latent image acts as areducing catalyst, whereby the light-insensitive silver salt is reducedto provide an image.

in the second embodiment of the present invention, the compound capableof becoming basic by heating provides the coating medium basicity andthe oxidation reduction potential of the reducing agent is lowered togive photographic activity theretofAccordingly, the exposed portion ofthe light-sensitive silver halide having a latent image acts as areducing catalyst to reduce the light-insensitive silver salt, wherebyan image is obtained.

Since the period of exposure is influenced by the kind and intensity ofthe light source and developing conditions, the kinds of reducing agentand other additives employed as well as the sensitivity of thelight-sensitive silver salt, it may vary by a considerably wide rangebut the deviation is generally from 0.001 second to 5 minutes.

The development of the thus-exposed light-sensitive ele ment isconducted by heating said element for l to 30 seconds at temperatureabove 80 (3., preferably from 120 C. to 170 C.

By immersing the thus heat-developed light-sensitive element in asolvent for the reducing agent such as water, the excess reducing agentand the like are removed from the emulsion layer. Thus, no reductionoccurs and hence even if the thus-treated light-sensitive element isexposed directly to sunlight, no density increase of the background isobserved.

Although the washing effect may usually be weak, methanol or ethanol maybe replaced with water for hastening the drying after the treatment.

If the developing temperature is comparatively higher, part or all ofthe reducing agent will be removed from the system by melting,evaporating or sublimating and hence even if the light-sensitive elementsubjected to the high-temperature development is allowed to stand as isor without the washing treatment, the density increase of the backgroundis scarcely observed or is not observed at all.

Further, the density increase of the background when exposed in a brightplace after development may be effectively prevented by incorporating inthe emulsion layer of the heatdevelopable light-sensitive element anoxidizing catalyst capable of destroying the reducing agent by heating,such as titanium oxide, stannic chloride, antimony chloride, galliumazide, cadmium sulfide, cadmium selenide, etc., in an amount of 0.1 to 5g. per 1 g. of the reducing agent.

As described above, since the light-sensitive elements of the presentinvention may be developed after exposure by the dry method and stableimages can be obtained without the need of conducting fixing and otherprocessing steps, it is now apparent that because of the presentinvention the reproduction process can be hastened and simplified.

Moreover, since the utilization of dry reproduction system eliminatesthe need of handling liquid chemicals for development and fixing, thereis the advantage that copies or reproductions can be directly obtainedin a dried state without being accompanied with the dangers ofcontaminating hands, clothes, etc., by handling liquid chemicals.

The following examples further illustrate the specific and preferredembodiments of the present invention.

EXAMPLE 1 Into a suitable amount of water were added 2 g. of the silversalt of benzotriazole, 7.5 g. of gelatin, 0.002 g. of strontium iodide,1 g. of morpholine oxalate, 25 g. of lead acetate trihydrate, and 0.5 g.of hydroquinone and the resulting emulsion was, after the furtheraddition of suitable amounts of a color sensitizer, an antifoggant, acoating aid, and a hardening agent, applied to a photographic paper.After exposure, the photographic element was developed by heating for 10seconds at C., immersed in tap water for 2 minutes, and dried. Thus, astable image causing no printout phenomena when exposed to directsunlight was obtained. Moreover, when the photographic element wasdeveloped, after exposure, by heating for 10 seconds at C. a stableimage causing no printout by direct exposure to sunlight was obtainedwithout the need of water washing.

EXAMPLE 2 The following coating compositions were applied successivelyto a photographic paper per 25 square meters thereof;

a. an aqueous solution containing 5 g. of gelatin and 4 g. of morpholineoxalate,

b. an aqueous solution containing 5 g. of gelatin and 20 g. of catechol,

c. an aqueous dispersion containing 50 g. of the silver salt ofbenzotriazole and g. of gelatin, and

d. an aqueous solution containing 10 g. of gelatin, 20 g. of leadacetate trihydrate, and 0.003 g. of cadmium chloride.

These coating liquids contained suitable amounts of a color sensitizer,a coating aid and a hardening agent.

After exposure, the resulting photographic element was developed byheating for 30 seconds at 160 C., immersed for 5 minutes in methanol andthen dried. Thus, a stable image causing no printout by direct exposureto sunlight was obtained.

EXAMPLE 3 into a suitable amount of water were added 2 g. of the silversalt of benzotriazole, 7.5 g. of gelatin, 0.0005 g. of silver iodide,2.5 g. of piperidine oxalate, 25 g. of lead acetate trihydrate, and 0.5g. of monomethyl hydroquinone and the resulting coating liquid was,after the further addition of suitable amounts of a color sensitizer, anantifoggant, a coating aid, and a hardening agent, applied to aphotographic paper.

The thus-obtained photographic element was developed by heating at 160C. for 10 seconds to provide a stable image causing no printout by thedirect exposure to sunlight.

EXAMPLE 4 into a suitable amount of water were added 2.5 g. of thesilver salt of benzotriazole, 7.5 g. of gelatin, 0.002 g. of bariumiodide, l g. of piperidine oxalate, and 25 g. of maltose and theresulting coating liquid was, after the further addition of a colorsensitizer, an antifoggant and a coating aid, applied to a photographicpaper. After exposure, the photographic element was developed by heatingfor seconds at 160 C., immersed in water for 10 minutes, and then dried.Thus, a stable image causing no printout by the direct exposure thereofto sunlight was obtained.

EXAMPLE 5 Into a suitable amount of water were added 1 g. of the silversalt of benzotriazole, 4.5 g. of gelatin, 0.03 g. of strontium iodide,0.5 g. of aluminum oxide, g. of lead acetate trihydrate, and 0.2 g. ofhydroquinone and the resulting coating liquid was, after the furtheraddition of suitable amounts of a color sensitizer, an antifoggant, acoating aid and a hardening agent, applied to a photographic paper per 2square meters thereof.

After exposure, the photographic light-sensitive element was developedfor 5 seconds at 160 C. to provide a reproduction showing almost nodensity increase of background when exposed to direct sunlight.Moreover, when the sample was immersed for more than 1 second in waterafter development followed by drying, a stable image causing no densityincrease by the direct exposure to sunlight was obtained.

EXAMPLE 6 The following coating compositions were successively appliedto a photographic paper per 25 square meters:

i. an aqueous dispersion containing 50 g. of gelatin and 5 g. of calciumhydroxide;

ii. an aqueous solution containing 5 g. of gelatin and 3 g. ofpyrogallol;

iii. an aqueous dispersion containing 15 g. of the silver salt ofbenzotriazole and 45 g. of gelatin; and

iv. an aqueous solution containing 50 g. of gelatin, 200 g. ofcadmium'acetate dihydrate, and 0.3 g. of barium chloride.

These coating liquids contained suitable amounts of a color sensitizer,a coating aid and a hardening agent. After exposure, the thus-preparedphotographic light-sensitive element was developed by heating for 30seconds at 140 C., immersed for 5 minutes in methanol and then dried.The thus-processed sample showed no background density increase whenexposed to direct sunlight.

EXAMPLE 7 Into a suitable amount of water were added 1 g. of the silversalt of benzotriazole silver, 4.5 g. of gelatin, 0.01 g. of silveriodide, 0.25 g. of aluminum oxide, 15 g. of zinc acetate, 0.2 g. ofmethyl hydroquinone, and 0.02 g. of titanium dioxide and the resultingcoating composition was, after the addition of suitable amounts of acolor sensitizer, an antifoggant, a coating aid and a hardening agent,applied to a photographic paper per 2 square meters thereof. Afterexposure, the thus-obtained light-sensitive element was developed for 5seconds at 150 C. When the thus-developed sample was exposed to directsunlight, no background density increase was observed.

EXAMPLE 8 The following coating liquids were applied in two layers to apolyethylene terephthalate film per 2 square meters thereof:

(Under layer) an aqueous dispersion containing 5 g. of gelatin and l g.of aluminum hydroxide and (Upper layer) an aqueous dispersion containingl0 g. of gelatin, 0.02 g. of potassium iodide, l g. of the silver saltof benzotriazole and 0.3 g. of hydroquinone.

These coating liquids further contained suitable amounts of a colorsensitizer, a coating aid and a hardening agent. After exposure, thethus-prepared light-sensitive element was developed by heating for 10seconds at 170 C. immersed in water for 5 seconds and then dried toprovide a stable image causing no background density increase whenexposed to direct sunlight.

EXAMPLE 9 Into a suitable amount of an aqueous acetic acid solution wereadded 2 g. of the silver salt of benzotriazole, 9 g. of ethyl cellulose,0.02 g. of strontium iodide, 0.5 g. of zinc oxide, 0.3 g. ofhydroquinone, and 0.01 g. of titanium dioxide and the resultingdispersion was, after the addition of suitable amounts of a colorsensitizer and an antifoggant, applied to a polyethylene terephthalatefilm per 4 square meters.

After exposure, the thus-obtained light-sensitive element was developedby heating for 10 seconds at C. to provide a reproduction causing almostno background density increase when exposed to direct sunlight.

EXAMPLE l0 Into a suitable amount of water were added l g. of the silversalt of benzotriazole, 9 g. of gelatin, 0.1 g. of strontium iodide, 0.6g. of hydroquione, and 2 g. of aluminum hydroxide and the resultingcoating composition was, after the addition of suitable amounts of acolor sensitizer, an antifoggant, a coating aid, and a hardening agent,applied to a photographic paper per 4 square meters.

After exposure, the thus-obtained light-sensitive element was developedby heating for 10 seconds at C. to provide a reproduction causing almostno background density increase when allowed to stand in situ in a brightplace.

We claim:

l. A heat-developable light-sensitive element comprising a supportbearing at least one layer thereon, said layer comprismg:

a. the silver salt of benzotriazole;

b. at least one member selected from the group consisting of a silverhalide and an inorganic halide represented by the formula MX,,, whereinM represents a member selected from the group consisting of a hydrogenatom, an ammonium group and a metal, X represents a halogen atom and nis the valency of M;

c. a. compound capable of releasing a basic material upon heatingcomprising at least one member selected from a group consisting of anoxalate of an organic amine, a metal oxide and metal hydroxide, saidmetal being a member selected from the group consisting of metals ofgroups 2 and 3 of the periodic table;

d. a compound containing water of crystallization; and

e. a reducing compound comprising a member selected from the groupconsisting of aromatic monoor polyhydroxyl compounds and derivativesthereof, and aromatic monoor poly-amino compounds and derivativesthereof.

2. The heat-developable light-sensitive element as in claim 1 whereinsaid oxalate of an organic amine is dicyclohexylamine oxalate,benzylamine oxalate, piperidine oxalate, or morpholine oxalate.

3. The heat-developable light-sensitive element as in claim 1, whereinsaid compound containing water of crystallization is a member selectedfrom the group consisting of lead acetate trihydrate, zinc acetatedihydrate and cadmium acetate dihydrate.

4. The heat-developable light-sensitive element as in claim 1 whereinsaid metal oxide is a member selected from the group consisting of zincoxide, aluminum oxide and magnesium oxide, and said metal hydroxide is amember selected from the group consisting of zinc hydroxide, aluminumhydroxide, cadmium hydroxide and magnesium hydroxide.

5. The heat-developable light-sensitive element as in claim 1, whereinsaid reducing agent is a member selected from the group consisting ofunsubstituted dihydroxybenzene, unsubstituted trihydroxybenzene,halogen-substituted dihydroxybenzene, alkyl-substituteddihydroxybenzene, said alkyl having one to four carbon atoms,aryl-substituted dihydroxybenzene, and l-phenyl-3-pyrazolidone.

6. The heat-developable light-sensitive element as in claim 1, whereinbased on 1 part by weight of said silver salt of benzotriazole, theproportion of said inorganic halide varies from 10" to 10" part byweight, the proportion of said silver halide varies from 10' to 10" partby weight, the proportion of said metal oxide varies from 20 to 10' partby weight, the proportion of said metal hydroxide varies from 20 to 10"part by weight, the proportion of said oxalate of an organic aminevaries from 10 to 10' part by weight, and the proportion of the reducingcompound varies from 20 to l part by weight.

7. A heat-developable light-sensitive element comprising a supporthearing at least one layer thereon, said layer comprismg:

a. the silver salt of benzotriazole;

b. at least one member selected from the group consisting of a silverhalide and an inorganic halide represented by the formula MX,,,.whereinM represents a member selected from the group consisting of ahydrogen atom, an ammonium group and a metal, X represents a halogenatom and n is the valency of M; a compound capable of releasing a basicmaterial upon heating comprising at least one member selected from agroup consisting of an oxalate of an organic amine, a metal oxide andmetal hydroxide, said metal being a member selected from the groupconsisting of metals of groups 2 and 3 of the periodic table; a compoundcontaining water of crystallization;

e. a reducing compound comprising a member selected from the groupconsisting of aromatic mono or poly hydroxyl compounds and derivativesthereof, and aromatic monoor poly-amino compounds and derivativesthereof; and

f. a catalyst for accelerating the oxidation of said reducing compound.

8. The heat-developable light-sensitive element as in claim 7, whereinsaid catalyst for accelerating the oxidation of the reducing compound isa member selected from the group consisting of titanium oxide, stannicchloride, antimony chloride, gallium azide, cadmium sulfide, and cadmiumselenide.

9. Therheat-developable light-sensitive element as in claim 7, whereinsaid reducing compound is a member selected from the group consisting ofunsubstituted dihydroxybenzene, unsubstituted trihydroxybenzene,halogen-substituted dihydroxybenzene, alkyl-substituteddihydroxybenzene, said alkyl having one to four carbon atoms,aryl-substituted dihydroxybenzene, and l-phenyl-3-pyrazolidone.

10. The heat-developable light-sensitive element as in claim 7, whereinbased on one part by weight of said silver salt of benzotriazole, theproportion of said inorganic halide varies from to 10 part by weight,the proportion of said silver halide varies from 10" to 10 part byweight, the proportion of said metal oxide varies from to 10 part byweight, the proportion of said oxalate of an organic amine varies from10 lit to 10" part by weight and the proportion of said reducingcompound varies from 20 to 10' part by weight.

111. A process for obtaining a print comprising exposing to light forfrom 0.001 second to 5 minutes a heat-developable light-sensitiveelement comprising a support bearing thereon at least one layercomprising:

a. the silver salt of benzotriazole; b. at least one member selectedfrom the group consisting of a silver halide and an inorganic haliderepresented by the fonnula MX,,, wherein M represents a member selectedfrom the group consisting of a hydrogen atom, an ammonium group and ametal, X represents a halogen atom and n is the valency of M;

c. a compound capable of releasing a basic material upon heatingcomprising at least one member selected from a group consisting of anoxalate of an organic amine, a

metal oxide and metal hydroxide, said metal being a member selected fromthe group consisting of metals of groups 2 and 3 of the periodic table;

. a compound containing water of crystallization; and

e. a reducing compound comprising a member selected from the groupconsisting of aromatic mono or polyhydroxyl compounds and derivativesthereof, and aromatic monoor poly-amino compounds and derivativesthereof; and heating the exposed element for a period of time of from 1to 30 seconds at a temperature of from to C.

112. A process for obtaining a print comprising exposing light for from0.001 second to 5 minutes a heat-developable light-sensitive elementcomprising a support bearing thereon at least one layer comprising:

a. the silver salt of benzotriazole;

b. at least one member selected from the group consisting of a silverhalide and an inorganic halide represented by the formula MX,,, whereinM represents a member selected from the group consisting of a hydrogenatom, an ammonium group and a metal, X represents a halogen atom and nis the valency of M;

c. a compound capable or releasing a basic material upon heatingcomprising at least one member selected from the group consisting ofdicyclohexylamine oxalate, benzylamine oxalate, piperidine oxalate,morpholine oxa late, a metal oxide and a metal hydroxide, said metalbeing a member selected from the group consisting of metals of group 2and 3 of the periodic table;

. a compound containing water of crystallization comprising a memberselected from the group consisting of lead acetate trihydrate, zincacetate dihydrate and cadmium acetate dihydrate; and

e. a reducing compound comprising a member selected from the groupconsisting of aromatic monoor polyhydroxyl compounds and derivativesthereof, and aromatic monoor poly-amino compounds and derivativesthereof; and heating the exposed element for a period of time of from Ito 30 seconds at a temperature of from I 20 to 170 C.

2. The heat-developable light-sensitive element as in claim 1 whereinsaid oxalate of an organic amine is dicyclohexylamine oxalate,benzylamine oxalate, piperidine oxalate, or morpholine oxalate.
 3. Theheat-developable light-sensitive element as in claim 1, wherein saidcompound containing water of crystallization is a member selected fromthe group consisting of lead acetate trihydrate, zinc acetate dihydrateand cadmium acetate dihydrate.
 4. The heat-developable light-sensitiveelement as in claim 1 wherein said metal oxide is a member selected fromthe group consisting of zinc oxide, aluminum oxide and magnesium oxide,and said metal hydroxide is a member selected from the group consistingof zinc hydroxide, aluminum hydroxide, cadmium hydroxide and magnesiumhydroxide.
 5. The heat-developable light-sensitive element as in claim1, wherein said reducing agent is a member selected from the groupconsisting of unsubstituted dihydroxybenzene, unsubstitutedtrihydroxybenzene, halogen-substituted dihydroxybenzene,alkyl-substituted dihydroxybenzene, said alkyl having one to four carbonatoms, aryl-substituted dihydroxybenzene, and 1-phenyl-3-pyrazolidone.6. The heat-developable light-sensitive element as in claim 1, whereinbased on 1 part by weight of said silver salt of benzotriazole, theproportion of said inorganic halide varies from 10 2 to 10 4 part byweight, the proportion of said silver halide varies from 10 2 to 10 4part by weight, the proportion of said metal oxide varies from 20 to 102 part by weight, the proportion of said metal hydroxide varies from 20to 10 2 part by weight, the proportion of said oxalate of an organicamine varies from 10 to 10 2 part by weight, and the proportion of thereducing compound varies from 20 to 10 2 part by weight.
 7. Aheat-developable light-sensitive element comprising a support bearing atleast one layer thereon, said layer comprising: a. the silver salt ofbenzotriazole; b. at least one member selected from the group consistingof a silver halide and an inorganic halide represented by the formulaMXn, wherein M represents a member selected from the group consisting ofa hydrogen atom, an ammonium group and a metal, X represents a halogenatom and n is the valency of M; c. a compound capable of releasing abasic material upon heating comprising at least one member selected froma group consisting of an oxalate of an organic amine, a metal oxide andmetal hydroxide, said metal being a member selected from the groupconsisting of metals of groups 2 and 3 of the periodic table; d. acompound containing water of crystallization; e. a reducing compoundcomprising a member selected from the group consisting of aromatic mono-or poly-hydroxyl compounds and derivatives thereof, and aromatic mono-or poly-amino compounds and derivatives thereof; and f. a catalyst foraccelerating the oxidation of said reducing compound.
 8. Theheat-developable light-sensitive element as in claim 7, wherein saidcatalyst for accelerating the oxidation of the reducing compound is amember selected from the group consisting of titanium oxide, stannicchloride, antimony chloride, gallium azide, cadmium sulfide, and cadmiumselenide.
 9. The heat-developable light-sensitive element as in claim 7,wherein said reducing compound is a member selected from the groupconsisting of unsubstituted dihydroxybenzene, unsubstitutedtrihydroxybenzene, halogen-substituted dihydroxybenzene,alkyl-substituted dihydroxybenzene, said alkyl having one to four carbonatoms, aryl-substituted dihydroxybenzene, and 1-phenyl-3-pyrazolidone.10. The heat-developable light-sensitive element as in claim 7, whereinbased on one part by weight of said silver salt of benzotriazole, theproportion of said inorganic halide varies from 10 2 to 10 4 part byweight, the proportion of said silver halide varies from 10 2 to 10 4part by weight, the proportion of said metal oxide varies from 20 to 102 part by weight, the proportion of said oxalate of an organic aminevaries from 10 to 10 2 part by weight and the proportion of saidreducing compound varies from 20 to 10 2 part by weight.
 11. A processfor obtaining a print comprising exposing to light for from 0.001 secondto 5 minutes a heat-developable light-sensitive element comprising asupport bearing thereon at least one layer comprising: a. the silversalt of benzotriazole; b. at least one member selected from the groupconsisting of a silver halide and an inorganic halide represented by theformula MXn, wherein M represents a member selected from the groupconsisting of a hydrogen atom, an ammonium group and a metal, Xrepresents a halogen atom and n is the valency of M; c. a compoundcapable of releasing a basic material upon heating comprising at leastone member selected from a group consisting of an oxalate of an organicamine, a metal oxide and metal hydroxide, said metal being a memberselected from the group consisting of metals of groups 2 and 3 of theperiodic table; d. a compound containing water of crystallization; ande. a reducing compound comprising a member selected from the groupconsisting of aromatic mono- or poly-hydroxyl compounds and derivativesthereof, and aromatic mono- or poly-amino compounds and derivativesthereof; and heating the exposed element for a period of time of from 1to 30 seconds at a temperature of from 120* to 170* C.
 12. A process forobtaining a print comprising exposing light for from 0.001 second to 5minutes a heat-developable light-sensitive element comprising a supportbearing thereon at least one layer comprising: a. the silver salt ofbenzotriazole; b. at least one member selected from the group consistingof a silver halide and an inorganic halide represented by the formulaMXn, wherein M represents a member selected from the group consisting ofa hydrogen atom, an ammonium group and a metal, X represents a halogenatom and n is the valency of M; c. a compound capable or releasing abasic material upon heatiNg comprising at least one member selected fromthe group consisting of dicyclohexylamine oxalate, benzylamine oxalate,piperidine oxalate, morpholine oxalate, a metal oxide and a metalhydroxide, said metal being a member selected from the group consistingof metals of group 2 and 3 of the periodic table; d. a compoundcontaining water of crystallization comprising a member selected fromthe group consisting of lead acetate trihydrate, zinc acetate dihydrateand cadmium acetate dihydrate; and e. a reducing compound comprising amember selected from the group consisting of aromatic mono- orpoly-hydroxyl compounds and derivatives thereof, and aromatic mono- orpoly-amino compounds and derivatives thereof; and heating the exposedelement for a period of time of from 1 to 30 seconds at a temperature offrom 120* to 170* C.